The platelet cytoskeleton: evidence for its structure from interactions with ZnCl2

Isolation of platelet membranes and cytoskeletons in the presence of ZnCl2 as a stabilization agent, suggests that the 255 kd mol. wt. actin-binding-protein (rather than the 100 kd alpha-actinin-like constituent) may be involved in linkage of cellular cytoskeletal constituents to 105- and 120-kd membrane glycoproteins (presumed to be GP IIb and IIIa). Lack of detection in these preparations of a constituent that binds RBC alpha-spectrin antibody plus the presence of significant quantities of actin, further suggests that the principal membrane skeletal element is actin with perhaps smaller quantities of a 240-kd component, identified by others as the protein talin. Electron micrographs of platelets that have adhered to, partially spread on a substrate in the presence of ZnCl2, and have been jet washed with buffer, suggest the presence in these cells of both a membrane skeleton and a transcellular cytomatrix. The relationships between the membrane, membrane skeleton, transcellular cytomatrix and platelet granules are depicted in a proposed model (Fig. 9).